Many internal combustion engines utilize cooperative engine cylinder and piston arrangements to generate power using a pumping motion. Engine cylinder and piston arrangements may be used to intake or scavenge an air-fuel mixture or strictly air charge (in fuel injected engines) for combustion and expel spent exhaust gases in multicycle operations, such as, for example, in 2-cycle and 4-cycle operations. While embodiments of the present invention have primary use for 2-cycle engine operation, the claims defining the invention are not limited to 2-cycle engines unless such limitation is expressly set forth in the claims.
Further, it is to be appreciated that the reference herein to an engine “cylinder” is not limited to a combustion chamber having a cylindrically shaped cross-section. Instead, the term cylinder refers to any combustion chamber or cavity provided in an internal combustion engine that receives a piston having an outer shape adapted to allow the piston to seal against the sidewall of the cylinder but at the same time permit the piston to slide back and forth reciprocally within the engine cylinder in a pumping motion.
In a fuel injected 2-cycle internal combustion engine, the engine cylinders may include one or more scavenging ports provided on the cylinder wall and one or more exhaust ports provided on the (usually opposite) side of the cylinder wall which permit gases to flow into, and out of, the engine cylinder, respectively. The pumping motion of the engine pistons may scavenge the air charge into the engine cylinder from the scavenging or intake port(s) for combustion and expel the spent charge exhaust gases generated from the previous combustion event through the exhaust port(s). In order to obtain efficient engine operation, the engine design, and specifically the engine piston and cylinder design, may minimize the flow of fresh, non-combusted air from the scavenging port(s) directly to the exhaust port(s). Improved engine efficiency may also result from an engine piston and cylinder design which: promotes swirl and turbulence in cylinder squish areas; permits central location of the spark plug, glow plug, water injector, and/or fuel injector over the piston in squish areas; and provides a shortened flame front propagation during combustion.
A known method of scavenging a two-cycle engine used a deflector structure or fin provided on the piston head to guide the incoming mixture as it entered the cylinder from a scavenging port. The deflector structure was provided to reduce the amount of the incoming charge that flowed across the cylinder head and out of the exhaust port before it was combusted. More specifically, the intended purpose of the deflector structure was to serve as a barrier to deflect the incoming charge upward away from the exhaust port in order to reduce the amount of incoming charge that escaped through the exhaust port before it was combusted.
Deflector structures on 2-cycle engine piston heads were replaced in many instances by flat piston heads that were required to obtain increased engine efficiency using higher compression ratios. The addition of known deflector structures limited the degree to which the piston could approach the upper cylinder wall, thereby limiting compression ratio. While a flat piston head permits higher compression ratio, it does not allow effective scavenging of the engine when compared with a traditional deflector or barrier fin based scavenging method; this is especially true in high compression diesel engines. Further, known deflector structures could create hot spots causing premature combustion of the charge and knocking. Such knocking can damage the engine in addition to causing further inefficiency by working against the advancing piston and the rotation of the crankshaft resulting in a definable loss of power.